Selecting system



w. H. T. HoLDEN SELECTING s YsTEM Filed Dee. so, 1941 Dec. 1, 1942. Y 2,303,356

2 Sheets-Sheet 1 /A/l/E/v To@ W. H. 7T HOLDEN ATTO/QN V w. H. T. HOLDEN 2,303,356

SELECTING SYSTEM Filed Dem.` 3o, 1941 2 sheets-sheet 2 NNN Dec. 1',I 1942,

Patented Dec. l, 1942 SELEGTING SYSTEM William H. T. Holden, Woodside, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 30, 1941, serial Ne. 424,866

6 Claims.

This invention relates to selecting systems and particularly to those used in the establishment of automatic telephone or other communication connections.

The objects of the invention are to minimize the number of false operations and double connections incident to the testing of links, trunks, cr other circuits used in automatic switching systems; to obtain a more positive test of these circuits; to enable the ready detection of an unstandard condition on the conductors over which these circuits are tested; to enable both the testing and switch-operating functions to be performed over the same conductors without danger of false operations; and to obtain other improvements and advantages in systems of this character.

In systems lof the well-known crossbar type where connections between incoming and outgoing circuits are performed at switching stages comprising a plurality of interconnecting channels, each of which includes a number of serially related links, it has been the common practice to use relays for testing the several channels provided for interconnecting any incoming trunk to any outgoing trunk. These relays are usually common to the switching stages and serve to determine the busy or idle condition of each of the individual links involved in each of the interconnecting channels.

In accordance with the present invention the testing relays of these prior systems are replaced by space-discharge tubes which are capable of distinguishing between links that have an idle condition on their test conductors and links that have their test conductors in a busy or an open condition or inadvertently crossed with other conductors. More speciiically, an alternating voltage source is applied to the test conductors of the component `links of each switching channelL ,condition for use, the alternating potential apf plied to the corresponding tube is suicient to operate it; whereas if the test conductor of the link has a busy condition thereon, or is open, or is crossed with some other conductor, the potential applied to the tube is insuiiicient to operate it.

Thus only if all links of a channel are idle, the corresponding tubes all operate and cause the operation of a single testing tube which is individually associated with the channel. This tube in turn causes the application of battery potention directly to the test conductors of all component links of the idle channel, andthe resultant current flow in these test conductors operates the switch magnets to seize the channel for use.

By using an alternating voltage and by prop;- erly selecting the impedances of the transformers with respect to that of the switch magnets, it is possible to test the condition of the links, without falsely operating the switch magnets, by applying this alternating voltage to the same link conductors over which the magnets are subsequently operated if the test indicates that the channel is idle. The advantage of this feature will be obvious; it reduces the number of conductors extending between the switch links and the common markers which perform the tests and apply the operating currents for energizing the switch magnets. Also a more positive test is obtained than is possible where relays are' used to test the links over the same conductors that serve as the operating circuits for the switch magnets.

These and other features of the'invention will be described more fully in the following 'specication:

Fig. 1 illustrates two frames of automatic switches through which connections are established. This figure also shows the frame connectors which serve to connect to these frames one ofA a number of common switch-controlling markers; and e Fig. 2'illustrates portions of one of these switchcontrolling markers.

Although the invention is applicable to testing arrangements for testing links, trunks or other circuits in variousftypes of communication systems, it has been disclosed herein for the purpose of illustration in a telephone system of the crossbar type.` In such a system connections are established through successive frames of crossbar switches, such as the district frame and the oce frame, by way of connecting channels, each of which comprises as many as three separate link circuits arranged in serial relation. Since kthese links are capable of being used in a plurality of different channels, it is necessary to test the component links of each channel capable of serving the particular call to determine which channels are idle, inlother words, to determine which channels have all of their component links in an idle condition.

In the system illustrated herein these matching tests are performed by electronic devices, such as space-discharge tubes, in the common marker, these tubes being associated respectively through the frame connectors with the connecting channels over which the call may be extended. The condition of the component links of each channel determines the potentials to be applied to the electrodes of the associated tube. tials are derived from a source of alternating voltage which is applied to the test conductors through the primary windings of transformers. Each transformer and the corresponding switchoperating magnet, both of which are connected to the link testing conductor, have Yimpedances which are so chosen that the resulting potential produced'on the test conductor is suicient to operate the associated discharge tube if the link is idle and is insucient to operate the tube if the linkis busy, if the test conductor is open, or if the test conductor is inadvertently connected to another test conductor. If all links of a particular channel are idle simultaneously, the corresponding tubes in the marker all operate and cause the application of a direct current source to the test conductors of these links to operate the associated magnets on the switch frames.

Referring particularly. to the drawings, two frames of crossbar switches` are illustrated, a district frame |00 and an oice frame |0|. It will be assumed that each of these frames comprises ten primary and ten secondary crossbar switches. One district primary switch, the No. 9 switch |02, and two district secondary switches, the No. 0 switch |03 and the No. 9 switch |04, are shown. The incoming trunks, such as trunk |05, appear in the horizontal rows of contacts of the primary switches, and the primary switches have access to the secondary switches by way of district links |06, |01. There are ten links appearing in the ten vertical rows of contacts of each .primary switch, and these ten links are distributed to the ten secondary switches, appearing in the horizontal rows of contacts of said secondary switches.

Two of the ten primary oice switches, the No. 0 switch |08 and the No. 9 switch |09, and one secondary office switch, the No. 9 switch ||0, are

illustrated. f

The one hundred office junctors appearing in the vertical contacts of the ten secondary Ydistrict switches are divided into -ten groups, each group leading to one of ten oflice frames.

and the ten ofce junctors ||2 extending fromlthe district frame |00 appear in the vertical rows of contacts of the ten primary oilice switches |08, |09. Similar junctor groups from VFor example, the oilice link H3 outgoing from the primary-switch |08 and the oflce link ||4 outgoing from the primary switch |09 appear in -the secondary switch ||0. IThe ten secondary oice switches have access to outgoing trunks,

ysuch as trunks ||5, ||6.

From the foregoing description it will be seen that there are ten possible channels between any These poten- Only one of these oil'ce frames |0| is shown in the drawings,

trunk incoming to a district primary switch and any trunk outgoing from an oflice secondary switch. Each one of these channels comprises a district link, an office junctor, and an office link in serial relation. For example, one channel extending from the district primary switch |02 to the secondary olce switch |0 comprises the district link |01, oillce junctor ||2, and the office link H4. Another channel between these switches comprises the district link |06, office junctor and the oftice link |3.

The common marker disclosed in Fig. 2 includes the testing mechanism whereby the oomponent links of the several channels are tested simultaneously vto determine which channels are available for use. This testing mechanism includes a plurality of groups of discharge tubes, one for each of the channels to be tested simultaneously, each group including three tubes which correspond respectivelyto the three links of the channel. Two of these groups are shown in the drawings, one of which includes the tubes 200, 20|, 202 and the other of which includes tubes 203, 204, 205. There may be as many of these groups as required. If,vfor example, it is desired to make a simultaneous test of ten different channels through the district and office frames |00 and |0l, ten groups of testing tubes would be provided in the marker. The testing mechanism also includes a plurality of groups of transformers, each group corresponding to one of the channels and including a transformer for each of the links in the channel. Transformers 206, 201 and 208 comprise the group corresponding to tubes 200, 20| and 202; and transformers 209, 2|0 and 2|| comprise a second group corresponding to tubes 203, 204 and 205. The primary winding of these transformers serves to connect a source of alternating voltage to the several test conductors. which are connectable individually to the test conductors of the links of the several channels to be tested simultaneously. For example, the primary windings 2|2, 2|3 and 2|4 of transformers 206, 201 and 200 interconnect the respective test conductors 2 I5, 2 6 and 2 1 through suitable condensers 2 |8, 2| 9 and 220 with the common supply conductor 22| to which the source of alternating voltage 222 is connected when the test is to be made. Similarly the primary windings of the transformers 209, 2|0 and 2| interconnect the test conductors 223, 224 and 225 with the common supply conductor 226 to which the source 222 is connectable. And the same is true of the other groups of transformers not shown on the drawings. The primary windings of the several transformers are shunted by condensers of suitable capacity, such as the condensers 221, 228 and 229 for the purpose of obtaining the desired impedance relation between the supply conductors 22| and the individual test conductors.

The several test conductors are connected through resistance elements to the starting electrodes of the respective tubes in order that the tubes may determine from the potential on these test conductors whether the corresponding links in the switch frames |00 and |0| are idle and in proper condition for use. To illustrate, it will be ynoted that the test conductors 2|5, 2|6 and 2|1 are joined respectively to the starting electrodes 230, 23| and 232 of the tubes 200, 20| and 202 through individual resistors 233, 234, 235. The

-main anodes 260, 26| andl 262 of these tubes are connected respectively to the secondary windings 235, 231 and 238 of the corresponding transformers. The cathodes 239, 240 and 24| of these tubes asoassc are connected through resistances 242, 243 and 244 tothe" negative pole of battery 245. Also these cathodes are connected through resistances 246, 241 and v248 and throughV thei'cor'nrnon resistance 249fto the-startingelectrode250 of the tube'25I, Which is common'to the group containing tubes 200, and'202. The anode 252 of the common tube is connected through the winding of relay 253 to the alternating current source 254. The cathode 255 of tube 25| is connected to the negative pole of battery 256.` .In a similar manner the anodes of tubes 203, 204 and 205 are connected to the secondary windings of the corresponding transformers, and the cathodes are connected through resistors to the negative pole of battery 25T and through other resistances to the starting electrode of the cornmon tube 258.

In order that the links of the frames |05 and ||l| may be tested by the marker shown in Fig. 2, the marker is connected at the appropriate time to these frames and to the particular switches on these frames on which the desired links appear. These connections are made by the frame connectors I|1,` IIS and IIS. The connector Ill comprises a multicontact relay I2!! for the marker illustrated, a similar relay for each other marker having access to the frame, a relay |2| forthe primary switch |02 and nine other similar relays for the nine remaining primary switches on vthe district frame. The connector ||8 comprises a multicontact relay |22 for the marker, corresponding relays for other markers, and yten relays, including the relay |23, onefor each of,y the ten groups of office junctors. cludes the marker relay |24, corresponding relays for other markers, and ten relays including relay |25, one for each of the oilice secondary Switches.`

The test of the three links comprising a channel, such as links |61, |I'2"and ||4, is made by connecting the alternating voltage source 222 overconductor 22| through the primary circuits of the transformers 206, 201 and 208 to the test conductors 2|5, 2I6 and 2|1, which in turn are connected respectively through the connectors II1, I8 and |I9'to the test conductors of the links |01, ||2 and II 4. It will be noted that the test conductor of the link |01 is also connected through the winding of the. associated operating of batteries I3| and |32, and that they test conductor of link I I4 is connected through the Winding of the operating magnet |29 to the negative pole of battery |33. If the link |51 is idle and the test conductor leading into the marker is con.- tinuous, the voltage of the alternating source 222 adds tothe voltage of battery |30., when the a1.- ternating source is in its positive half cycle, and causes current to ovv in the test conductor 2|5. The potential on the conductor 2 |,5 depends, upon the relative impedances of the primary circuitl of transformer 206 and the winding of the operatingmagnet |26. These impedances are so chosen, preferably at about equal values, that the potential appearing on the conductor lI5 is suiiicient to ionize the operating gap of the tube f resistor 23.3, to theA start elftlQSo. 2310 alla. @Q95 l,

The connector |I3 into the potential of the battery 245 applied to the cathode 239. Hence the starting gap 230-239 y ionizes if the link |01 is idle and the test conductor is closed and is free ,from cross connections. If, however, the link |31 is busy, a ground potential exists on the test conductor, and no potential is applied to' the starting electrode 230 of the tube 200. Similarly if the link I 01 is idle and an open condition exists in the test conductor eX- tending into the marker, no potential is applied to the electrode 230 from the link. Again if the link I |31 is idle and the test conductor is continuous but is inadvertently crossed with some other conductor, Vsuch asy the test conductor |34, the parallel connections through the impedances of the two operating magnets serves to lower the resultant potential on conductor 2|5 and on the electrode i230 below the Value necessary to ionize the control gap 23S- 239 of the tube 200. Therelfore, the test tube 200 will operate its control gap only if the link |521 is idle and its test conductor is free from all unstandard conditions. In a similar manner the tubes 20| and 202 test the condition of the links l I2 and I4.

If the tube 200 operates its control gap to indica-te that the link |$1 is idle and in proper condition to be selected for use, the main gap of the tube immediately discharges. 'I'he source of current for the main discharge gap of the tube is supplied by the voltage induced in the secondary winding 235 of the transformer 206 on each positive half cycle and by the battery 245 connected to the cathode 239. The circuit for this current flow may be traced from the upper terminal of the secondary winding 236, anode 250, cathode 239, resistor 242 to the negative pole of battery 245. If the link I I2 is idle and tube 20| ionizes its control gap, the main discharge gap is immediately ionized, and current flows from the upper terminal of windingl 231 on each positive half cycle, anode 23|, cathode 2430, resistor 243 to the negative pole of battery 245. Similarly if the third link ||4 is idle, the tube i12 ionizes, and current flows in the main discharge gap including the anode 262,

cathode Zal, resistor 244 to the negative pole of battery 245. Thus if all three tubes are operated, the voltages developed across the resistors 242, 2543 and 244 are equal and no current flows in resistors 245, 241 and 248. Accordingly the full positive potential on the cathodes 230, 240 and 24| is applied through resistors 246, 241 and 248 in parallel through the common resistor 243 to the starting electrode 250 of the tube 25|, This positive potential adds to the negative potential of battery 255, and the control gap Z-255 ionizes. At the time the control gap of the tube 25| ionizes, the source 254 is in its positive half cycle, and current flows from said source through the upper winding of relay 253, anode 252, cathode 255 to the negative pole of battery 256. The relay V251i operates in this circuit and performs the functions to be explained hereinafter.

Thus if all three of the tubes 230, 20| and 222 operate, indicating that the corresponding links |01, |52 and H4 of the channel are all idle, the common tube 25| receives sufficient potential on its starting electrode 25S to operate, However, if only two of the links are idle and the third one, say the link H4, is busy, the tube 25| fails to operate. Since the link H4 is busy, the tube 2t?. remains deionized, and no voltage is developed across the resistor 244, Therefore, the voltage across resistors 242 and 243 cause current to flow in obvious circuits through the resistors 246 and 241 and resistors 248 and 244,' This current flow in resistors 246 and 241 lowers the potential applied to the electrode 250 below the point where it is sufcient to ionize the tube 25|. Similarly if only one link, link |01, is idle, the tubes 26| and 202 remain deenergized, and no voltages are developed across resistors 243 and 244. Consequently the voltage across the resistor 242, resulting from the operation of tube 200, causes current to flow through resistor 246 and thence in parallel through the resistors 241, 243 and 248, 244. This flow of current in the resistor 246 lowers the potential applied to electrode 250 below the ionizing value, and the tube 25| fails to operate.

In a similar manner simultaneous tests are made of all other channels to which the marker is connected, and the common tubes 25|, 258, etc., corresponding to all idle channels are ionized, whereas the common tubes relating to all channels having one or more busy links or one or more links in an unstandard condition fail to ionize. If at the time this test is made the other channel illustrated is idle, namely the channel comprising links '|06, and ||3, the associated tubes 203, 204 and 205 are operated, and the common tube 258 operates to cause the energization of relay 263 in a circuit including the source 264.

Since only one idle channel is needed for setting up the desired connection, means is provided for choosing the first idle channel and excluding all other channels that may be found idle at the time. This means includes the common slow-releasing relays 265 and 266. As soon as relay 253 operates, a holding circuit is closed therefor traceable from battery through the lower winding of the relay, front contacts of said relay to ground at the back contacts of relay 266. Relay 253 in operating opens the holding circuit of relay 263 andof all other succeeding relays, Therefore, relay 253 is the preferred one, and the channel it represents will always be chosen in preference to other channels. Also when relay 253 operates, it opens the original circuit from the source 222 to the conductor 22|. Before this circuit is opened, however, the relay 253 locks itself in the holding circuit above described. Relay 253 operates relay 265, which in turn operates relay 266. Relay 265 disconnects the source 222 from conductor 261 to cause the release of all tubes that may have been operated in connection with other idle channels. When relay 266 operates it opens the holding circuit of relay 253. During the interval that relay 253 is maintaining its armature in a closed condition circuits are closed for operating the magnets associated with the links |01, ||2 and ||4 of the third idle channel. The circuit for magnet |26 may be traced from ground through the front contact of relay 266, armature and front contact of relay 253, conductor 268, conductor 2|5, contacts of relays |20 and |2|, test conductor |01 through the winding of magnet |26 to the negative pole of battery |30. The circuit for magnets |21 and |20 may be traced from ground through the front contact of relay 266, armature and front contact of relay 253, conductor 269, conductor 2|6 thence through the contacts of relays |22 and |23, conductor ||2 and in parallel through the windings of magnets |21 and |28 to battery and ground. Similarly the operating circuit for magnet |29 is closed through the contacts of relay 266 and relay 253, After an 'interval relay 253 releases and causes the release in turn of relays'265 and 266. The commoncontrol circuit is now restored so that tests may be made of the channels.

It will be noted that the vtest circuit for the district link |01 includes the primary winding of the transformer 206 and the winding of the operating magnet |26. As mentioned hereinbefore the impedances of the transformer and the magnet are proportioned so as to provide the necessary potential on the conductor 2|5 for identifying the condition of the district link. For example, the impedance of the primary transformer winding may be substantially equal to the impedance of the magnet |26, in which case the voltage lis divided equally across these impedances. The same is true of the test circuit for the office link ||4, which includes the primary winding of transformer 208 and the winding of the operating magnet |29. Since however the intermediate link ||2 is connected to both magnets |21 and l|28 in parallel, it is necessary, of course, to select the impedances of these magnets and the impedance of the transformer 201 to provide the same potential on conductor 2|6 that exists on conductors 2|5 and 2|1 for the same condition. This may be done by making the impedance of the primary of transformer 201 onehalf as great as that of the primary windings of the other transformers.

For a more complete understanding of the details of the crossbar system and the operation of the switches and markers, reference may be had to the patent to Carpenter, 2,235,803 of March 18, 1941. The discharge tubes disclosed herein may be of any well-known type, such as those having gas-lled envelopes and cold cathodes.;

What is claimed is:-

1. In combination, a plurality of connecting channels each comprising a number of serially related links, operating magnets for saidv links for connecting the links of any channel in series, test conductors, means for connecting the test conductors individually to the separate links of a channel and to the operating magnets of said links, impedance devices connected individually in said test conductors, a group of discharge tubes for each channel including a tube for each link of the channel, circuits for connecting said tubes to the corresponding test conductors, a source of test voltage and means for applying the same through said impedance devices to the several test conductors, the impedance of said devices being so proportioned with respect to the impedance of said magnets that the resulting potential on each of said test conductors is suicient to operate the associated tube if the corresponding link is idle and insuiiicient to operate the tube if the link is busy, and means responsive to the operation of all tubes of a group representing the idle links of a channel for operating the corresponding magnets to establish a connection over the links of said channel in series.

2. In combination, a plurality of connecting channels each comprising a number of serially related links, operating magnets for said links for connecting the links of any channel in series, test conductors, means for connecting the test conductors individually to the separate links of a channel and to the operating magnets of said links, transformers each having one Winding connected individually in one of said test conductors, a group of discharge tubes for each channel including a tube for each link thereof, circuits for connecting each of said tubes to the-corresponding test conductor and to the other Winding of the corresponding transformer, a source of test voltage, and means for applying the same through one of the windings of each of said transformers to the several test conductors, the impedance of said transformers and the impedance of said operating magnets being chosen to produce a resulting potential on each of said test conductors suilicient to operate the associated tube if the link is busy, and means responsive to the operation of all tubes of a group representing the idle links of a channel for operating the corresponding magnets to establish a connection over the links of said channel.

3. In combination, a plurality of connecting channels each comprising a number of serially related links, operating magnets for said links for connecting the links of any channel in series, test conductors, means for connecting the test conductors individually to the separate links of a channel and to the operating magnets of said links, impedance devices connected individually in said test conductors, a group of discharge tubes for each channel including a tube for each link of the channel, circuits for connecting said tubes to the corresponding test conductors, a source of alternating voltage, and means for applying the same through said impedance devices to the several test conductors, the impedance of said devices being so related to the impedance of said magnets that the potential produced on each of said test conductors in response to the application of said alternating voltage is sufficient to operate the associated tube if the corresponding link is idle and insumcient to operate the tube if the link is busy, and means responsive to the operation of the tubes of a group representing the idle links of a channel for operating the corresponding magnets to establish a connection.

4. In combination, a plurality of connecting channels each comprising a number of serially related links, operating magnets for said links for connecting the links of any channel in series, test conductors, means for connecting the test conductors individually to the separate links of a channel and to the operating magnets of said links, impedance devices connected individually in said test conductors, a group of discharge tubes for each channel including a tube for each link of the channel, circuits for connecting said tubes to the corresponding test conductors, a source of test voltage and means for applying the same through said impedance devices to the several test conductors, the impedance of said devices and the impedance of said magnets serving to divide the applied test voltage to produce on each of said test conductors a resulting potential sufiicient to operate the associated tube if the corresponding link is idle and insuflcient to operate the tube if the link is busy, if the test conductor is open, or if the test conductor is inadvertently connected to some other test conductor, and means responsive to the operation of the tubes representing the idle links of a channel for operating the corresponding magnets to establish a connection.

5. In combination, a plurality of connecting channels each comprising a number of serially related links, operating magnets for said links for connecting the links in any channel in series, each of said links having a test conductor connected to the corresponding operating magnet, a plurality of impedance devices, means for connecting said impedance devices individually to the test conductors of said links, discharge tubes, one for each of said impedance devices, circuits for connecting said tubes respectively to the corresponding impedance devices and to the corresponding test conductors, a source'of alternating voltage, means for applying the same through said impedance devices to the several test conductors, said impedance devices and said operating magnet serving to divide the applied voltage to produce a-resulting potential on each of said test conductors suiicient to operate the associated tube if the corresponding link is idle and insuiicient to operate the tube if the link is busy, a source of direct current, and means responsive to the operation of the tubes corresponding to the idle links of a channel for connecting said source of direct current to the test conductors of said idle links for operating the associated magnets to establish a connection.

6. The combination in a telephone system of a trunk circuit for extending telephone connections, a test conductor for said trunk circuit, means for varying the impedance of said test conductor in accordance with the busy or idle condition of said trunk, a testing mechanism including a source of alternating current, means for connecting said source of alternating current to said test conductor, means in said mechanism for measuring the impedance of said test conductor when said source is connected thereto, an electronic device in. said mechanism operative in response to the impedance measurement when said trunk is in an idle condition, and means controlled by said electronic device for establishing a connection over said trunk.

WILLIAM H. T. HOLDEN. 

